The present invention relates to a control system for an internal combustion engine having a turbocharger drivable by the energy of exhaust gases emitted from the engine, and more particularly to a control system for an internal combustion engine, especially a gasoline engine, having a turbocharger combined with an electric rotary machine serving as a motor-generator mounted on the rotatable shaft of the turbocharger.
Japanese Laid-Open Patent Publication No. 60-195329 discloses an engine system in which an electric rotary machine operable as a motor or a generator is mounted on the rotatable shaft of a turbocharger drivable by the energy of exhaust gases emitted from an engine, and the electric rotary machine is operated as a motor or a generator dependent on operating conditions of the engine.
According to the disclosed arrangement, when the engine rotates at a low speed and under a high load, the electric rotary machine is operated as a motor to assist in turbocharging the engine. With a gasoline engine, unlike a diesel engine, the boost pressure produced by the turbocharger is increased up to a region upstream of a throttle valve. When the engine is under a partial load, however, the opening of the throttle valve is reduced, and the pressure near an intake valve is made lower than the atmospheric pressure.
In case the electric rotary machine is operated as a motor with the turbocharged boost pressure used as a reference, since the pressure of intake air supplied to the engine is low, no optimum engine output power is available when the engine is partially loaded.